Docker is an open source project to pack, ship,
and run any application as a lightweight, portable, self-sufficient container.
When you deploy an app with gitpush or tsuruapp-deploy, tsuru builds
a Docker image and then distributes it as units (Docker containers) across
your cluster.

A unit is a container. A unit has everything an application needs to run; the
fetched operational system and language level dependencies, the application’s
source code, the language runtime, and the application’s processes defined in
the Procfile.

A platform is a well-defined pack with installed dependencies for a language or
framework that a group of applications will need. A platform might be a
container template (Docker image).

For instance, tsuru has a container image for Python applications, with
virtualenv installed and other required things needed for tsuru to deploy
applications on top of that platform. Platforms are easily extendable and
managed by tsuru. Every application runs on top of a platform.

A service is a well-defined API that tsuru communicates with to provide extra
functionality for applications. Examples of services are MySQL, Redis, MongoDB,
etc. tsuru has built-in services, but it is easy to create and add new services
to tsuru. Services aren’t managed by tsuru, but by their creators.